Revision a82c25c366b0963d33ddf699196e6cf57f6d89b1 authored by Florian Westphal on 08 March 2022, 12:52:11 UTC, committed by Florian Westphal on 08 March 2022, 12:52:11 UTC
This reverts commit 878aed8db324bec64f3c3f956e64d5ae7375a5de. This change breaks existing setups where conntrack is used with asymmetric paths. In these cases, the NAT transformation occurs on the syn-ack instead of the syn: 1. SYN x:12345 -> y -> 443 // sent by initiator, receiverd by responder 2. SYNACK y:443 -> x:12345 // First packet seen by conntrack, as sent by responder 3. tuple_force_port_remap() gets called, sees: 'tcp from 443 to port 12345 NAT' -> pick a new source port, inititor receives 4. SYNACK y:$RANDOM -> x:12345 // connection is never established While its possible to avoid the breakage with NOTRACK rules, a kernel update should not break working setups. An alternative to the revert is to augment conntrack to tag mid-stream connections plus more code in the nat core to skip NAT for such connections, however, this leads to more interaction/integration between conntrack and NAT. Therefore, revert, users will need to add explicit nat rules to avoid port shadowing. Link: https://lore.kernel.org/netfilter-devel/20220302105908.GA5852@breakpoint.cc/#R Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2051413 Signed-off-by: Florian Westphal <fw@strlen.de>
1 parent f8e9bd3
atomic_bitops.txt
=============
Atomic bitops
=============
While our bitmap_{}() functions are non-atomic, we have a number of operations
operating on single bits in a bitmap that are atomic.
API
---
The single bit operations are:
Non-RMW ops:
test_bit()
RMW atomic operations without return value:
{set,clear,change}_bit()
clear_bit_unlock()
RMW atomic operations with return value:
test_and_{set,clear,change}_bit()
test_and_set_bit_lock()
Barriers:
smp_mb__{before,after}_atomic()
All RMW atomic operations have a '__' prefixed variant which is non-atomic.
SEMANTICS
---------
Non-atomic ops:
In particular __clear_bit_unlock() suffers the same issue as atomic_set(),
which is why the generic version maps to clear_bit_unlock(), see atomic_t.txt.
RMW ops:
The test_and_{}_bit() operations return the original value of the bit.
ORDERING
--------
Like with atomic_t, the rule of thumb is:
- non-RMW operations are unordered;
- RMW operations that have no return value are unordered;
- RMW operations that have a return value are fully ordered.
- RMW operations that are conditional are unordered on FAILURE,
otherwise the above rules apply. In the case of test_and_{}_bit() operations,
if the bit in memory is unchanged by the operation then it is deemed to have
failed.
Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics and
clear_bit_unlock() which has RELEASE semantics.
Since a platform only has a single means of achieving atomic operations
the same barriers as for atomic_t are used, see atomic_t.txt.
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